I. Seismotectonics of the San Jacinto fault zone and the Anza seismic gap. II. Imaging the shallow crust in volcanic areas with earthquake shear waves
Details are presented of the small earthquake stress release near Anza. Earthquakes define an 18-km quiescent segment of fault which is bounded by areas of high seismicity. Moderate earthquakes with few aftershocks indicate that the fault is seismogenic and highly stressed but locked, possibly due to high normal stresses. An earthquake swarm occurred recently near the gap in an area which was previously active before two nearby M greater than or equal to 6 earthquakes. This suggests that the swarm area may signal the presence of high stresses. Variations are investigated in the depths of earthquakes in the San Jacinto-southern San Andreas fault region. The maximum depth of earthquakes progressively shallows from 20 to 10 km towards the Imperial Valley region of high heat flow. Earthquakes occur predominantly in a band along the bottom of the seismogenic zone; few earthquakes occur in the shallower fault zone. This implies that shear stresses are greater deep in the brittle fault zone, and that loading of the brittle crust occurs along aseismic extensions of the fault zones. Deeper earthquakes in the region occur principally in the major fault zones, and shallow earthquakes occur principally in the adjacent crust. In Part II-S-wave seismograms are used to image attenuation structure in the crust of the Coso geothermal region of California. Forward modeling and inversion illuminate regions in the shallow crust which severely attenuate S waves. Surprisingly, these lie south of Coso beneath Indian Wells Valley. They are coincident with the epicentral locations of migrating earthquake swarms. No attenuating effects were seen beneath Coso above 5 km depth.
- Research Organization:
- California Inst. of Tech., Pasadena (USA)
- OSTI ID:
- 5953808
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Anomalous shear wave attenuation in the shallow crust beneath the Coso volcanic region, California
Internal structure of the San Jacinto fault zone at Jackass Flat from data recorded by a dense linear array
Related Subjects
15 GEOTHERMAL ENERGY
CALIFORNIA
GEOLOGIC FAULTS
GEOTHERMAL RESOURCES
STRESS ANALYSIS
SEISMIC SURVEYS
COSO HOT SPRINGS
DEPTH
EARTHQUAKES
GEOLOGIC DEPOSITS
IMAGES
SEISMIC EVENTS
SEISMIC S WAVES
SEISMICITY
SEISMOGRAPHS
STRESS RELAXATION
STRESSES
TECTONICS
VARIATIONS
DIMENSIONS
FEDERAL REGION IX
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
MEASURING INSTRUMENTS
NORTH AMERICA
RELAXATION
RESOURCES
SEISMIC ARRAYS
SEISMIC DETECTORS
SEISMIC WAVES
SURVEYS
USA
580201* - Geophysics- Seismology & Tectonics- (1980-1989)
150301 - Geothermal Exploration & Exploration Technology- Geophysical Techniques & Surveys